An electrophotographic or electrostatic image forming apparatus generally forms an image by taking the following steps: forming an electrostatic latent image on a photoreceptor, developing the electrostatic latent image into a toner image with a toner, transferring the toner image onto a recording medium, and fixing the toner image thereon by application of heat.
Toners are required to be fusible at much lower temperatures to meet recent demand for energy saving.
In place of vinyl resins having been widely used as toner binder, polyester resins are widely used recently because they are fusible and fixable on a recording medium at much lower temperatures. For example, Japanese Patent Application Publication No. 11-249339 proposes a toner including a crystalline polyester for the purpose of improving low-temperature fixability.
Generally, low-temperature fixability of toner can be improved by lowering the softening point of the toner, however it degrades heat-resistant storage stability. Such low-softening-point toner also contaminates and degrades developing members and carriers.